如何将__len__添加到sqlalchemy声明性元？

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String

Base = declarative_base()

class MyModel(Base):
    __tablename__ = 'my_table'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    
    def __len__(self):
        # 自定义的__len__方法实现
        # 返回模型对象的长度或其他计算逻辑
        pass

# 创建数据库引擎和会话
engine = create_engine('数据库连接字符串')
Session = sessionmaker(bind=engine)
session = Session()

# 查询数据并调用__len__方法
my_model = session.query(MyModel).first()
length = len(my_model)